1. Field of the Invention
This invention pertains to the field of digital signal processing and, in particular, to the matrix multiplication of a plurality of digital signals by a coefficient matrix of the type used in color video signal processing.
2. Background Art
Correction matrices are useful in a variety of color video applications. For instance, a conversion matrix is used to convert red, green, and blue video signals into Y (luminance) and I, Q (chrominance) signals. A color correction matrix is used to correct the spectral sensitivities of a video camera for the chromaticities of the phosphor set of the particular display in use. Another use is with film-to-video conversion, a process in which a color correction matrix operates on the film scanning signals to correct the film colorimetry for video display.
It is desirable for reasons of space and efficiency to implement the matrix in one, or a few, integrated circuits. A conventional approach is to use an array of multipliers, say nine multipliers, to implement a 3.times.3 matrix. This uses a prohibitive amount of circuit area (on an integrated circuit). The multipliers can be replaced with ROM (read only memory) look-up tables. This still takes too much area. Another approach approximates the matrix coefficients by simple shifting operations, which can be implemented digitally by "hardwired" right (or left) shift connections between registers that provide a "binary" matrix coefficient series, such as 1/32, 1/16, 1/8, 1/4, 1/2, 1, 2, etc. Such poor coefficient accuracy can be improved by summing selected coefficients, but this requires many adders and many shifts. Once again, too much area is required.
In U.S. Pat. No. 4,507,676, a compromise solution is disclosed in which each coefficient is broken into two parts: a binary part and a remainder. The binary part is implemented by a "hardwired" right shift and the remainder is implemented by a ROM look-up table. While such an approach provides additional accuracy, it would be desirable to eliminate the ROM look-up tables altogether. Moreover, in view of the disparate applications for video matrices, it would be greatly preferred to have a universal matrix chip that could be used for a variety of applications with a minimum of redesign.